(1) Field of the Invention
The present invention relates to an image forming apparatus such as a copier, facsimile machine, printer or the like and a toner supply control program used for the apparatus. In particular, the present invention relates to an image forming apparatus for performing image forming using a dual-component developer consisting of a toner and a carrier and a toner supply control program used for the apparatus.
(2) Description of the Prior Art
Conventionally, in an image forming apparatus of electrophotograpic type such as a copier, facsimile machine, printer and the like, a photoreceptor drum as an image support is uniformly electrified by a charger device, then an electrostatic latent image is formed on the photoreceptor drum. This electrostatic latent image is developed by the developing device and visualized into a toner image, which in turn is transferred to a recording medium in the transfer station. Then the recording medium is conveyed through the fixing unit, where the toner image is fixed to the recording medium, and is output as a printed image.
In the thus configured image forming apparatus, when a dual-component developer consisting of a toner and a carrier is used as its developer, only the toner is consumed for image forming, so that it is necessary to keep the toner concentration in the developing unit constant.
To deal with this, the image forming apparatus using the dual-component developer usually includes: a toner concentration sensor such as a sensor for detecting the toner concentration in the developer, a sensor for detecting the density of the toner image formed on the photoreceptor drum or the like; and a toner supply device for supplying toner from a toner supply container into the developing device in accordance with a detected signal issued when the fact that the toner concentration has fallen to a reference level or lower is detected by the toner concentration sensor, so that a suitable amount of toner is supplied in accordance with the amount of toner that has been used as image output has proceeded.
As for the above toner supplying techniques, some proposals have been made conventionally. For example, there is a proposal in which, the recording width L on the photoreceptor drum is divided into N blocks and the number of pixels to be written in for every width L/N is summed up and stored in association with the developer's speed of movement, Vz, in the axial direction of the developing roller, so as to estimate the amount of toner consumption, to thereby achieve toner supply without using any toner concentration detecting sensor (patent document 1: Japanese Patent Application Laid-open Hei 9 No. 160364). There is also another proposal in which, a plurality of toner loading ports for toner supply are arranged along the axial direction of the developing roller, and toner is loaded to the areas where toner has been consumed, through the ports where toner has been consumed more greatly to thereby keep the toner concentration constant (patent document 2: Japanese Patent Application Laid-open No. 2001-183894).
However, as to patent document 1, there is a fear that the error of toner concentration will build up since no toner concentration detecting sensor is used, and there is the problem of the accuracy of estimation of the toner consumption being not good enough since the number of pixels is counted line by line. There is also the problem that no leveling off of the toner concentration from the neighboring blocks due to toner agitation is considered.
On the other hand, in patent document 2, since the toner supply device has a complicated configuration, there is the problem and concern that the toner loaded through multiple toner loading ports cannot be agitated sufficient enough.